Oil canning is one of the most common (and frustrating) issues in trailer manufacturing. If you’ve ever noticed wavy, distorted panels on a cargo or enclosed trailer, you’ve seen oil canning in action.

For engineers, OEMs, and trailer manufacturers, understanding what causes oil canning, how it impacts performance, and how to prevent it is critical when selecting the right trailer siding material.

In this article, we’ll break down:

• What oil canning is

• Why it happens in aluminum and low-cost composite panels

• How it affects trailer performance and appearance

• How PolyCor™ AP composite trailer siding eliminates this issue

What Is Oil Canning in Trailer Panels?

Oil canning refers to the visible waviness or distortion that appears in flat metal or composite panels, especially large surfaces like trailer siding. The term comes from the way the panel flexes in and out, similar to pressing on the bottom of an old oil can.

It is most commonly associated with:

• Aluminum trailer siding

• Thin-gauge metal panels

• Low-quality composite panels

What Causes Oil Canning?

Oil canning is primarily caused by thermal expansion and contraction. Key causes include:

• Temperature fluctuations: Trailers experience extreme heat and cold, from hot highways to freezing storage conditions.

• Material movement: Aluminum expands when heated and contracts when cooled, leading to stress across large panels.

• Panel size and thickness: Larger, thinner panels are more prone to visible distortion.

• Improper installation or fastening: Uneven tension or spacing can amplify the effect.

• Low-quality materials: Cheap composite panels often lack the structural integrity to resist movement.

Over time, repeated expansion and contraction causes panels to lose their flatness, resulting in permanent waviness.

Why Is Oil Canning a Problem for Trailers?

Oil canning isn’t just a cosmetic issue; it can impact performance, branding, and long-term durability.

Why Aluminum Trailer Siding Is Prone to Oil Canning

Aluminum has long been a go-to material for trailer siding due to its lightweight properties, but it comes with tradeoffs. Common challenges with aluminum panels include:

• High thermal expansion: Aluminum expands and contracts significantly with temperature changes.

• Visible surface distortion: Even minor movement becomes noticeable across large, flat panels.

• Weight considerations: Standard 0.050" aluminum is approximately 25% heavier than PolyCor AP.

• Long-term performance concerns: Repeated movement can lead to surface inconsistencies, reduced aesthetic quality, and increased maintenance.

Because of these limitations, many OEMs and trailer manufacturers are actively searching for alternatives to aluminum trailer siding.

Are All Composite Trailer Panels Better?

Not necessarily. As demand for composite trailer siding panels grows, lower-cost alternatives have entered the market. While they may appear similar to premium materials, they often lack the engineering required to perform in demanding environments. These materials may still experience oil canning or similar distortions, especially over time.

How PolyCor AP Eliminates Oil Canning

Piedmont Plastics developed PolyCor AP to specifically address the limitations of aluminum and low-quality composites.

Engineered for Stability

Unlike aluminum, PolyCor AP is designed to maintain dimensional stability across temperature changes. This results in minimal expansion and contraction, reduced internal stress, and consistently flat panels.

Smooth, Flat Exterior Surface

PolyCor AP helps trailers maintain a clean, professional appearance, uniform surface across large panels, and high-quality finish over time. This is especially important for cargo trailer manufacturers, enclosed trailer OEMs, and specialty vehicle builders.

Benefits of PolyCor AP for Trailer Manufacturers

1. Oil Canning Resistance

The most significant advantage of PolyCor AP is its ability to prevent waviness and distortion, even in extreme environments.

2. Lightweight Performance

PolyCor AP averages 0.58 lbs/ft² per sheet, making it:

• Lighter than traditional aluminum

• Easier to handle and install

• Beneficial for overall trailer weight reduction

3. Enhanced Appearance for Graphics

A smooth surface ensures:

• Clean vinyl application

• Accurate branding

• Professional finished products

4. Durable Polyester Paint System

PolyCor AP panels feature a high-performance polyester coating that provides:

• Long-term durability

• Weather resistance

• Easy maintenance

5. Consistent Long-Term Performance

Because it resists movement, PolyCor AP helps:

• Reduce maintenance issues

• Improve product lifespan

• Deliver consistent results across builds

Why Manufacturers Are Switching to Composite Trailer Siding

The shift from aluminum to advanced composites like PolyCor AP is driven by a need for improved surface quality, reduced maintenance, better performance in varying climates, and enhanced branding capabilities. For OEMs, the goal is simple: deliver a product that looks better, lasts longer, and performs reliably.

Choosing the Right Trailer Siding Material

When evaluating materials, engineers and purchasers should consider:

• Resistance to oil canning

• Thermal stability

• Weight

• Surface quality

• Long-term durability

• Ease of installation

Working with an experienced supplier ensures you select a material that meets both performance and cost expectations.

Work with Piedmont Plastics

Piedmont Plastics is the exclusive distributor of PolyCor AP, providing trailer manufacturers with a proven solution to oil canning and siding instability. If you’re looking to eliminate oil canning and improve the quality of your trailer builds, PolyCor AP offers a reliable, engineered solution.

With local inventory, technical expertise, and a network of branches across North America, Piedmont Plastics helps OEMs and fabricators find the right materials for their applications. Get in touch with our sales team today for more information!